fix: resolve ESP32-S3 linker errors, all boards produce firmware

Three fixes:
- Add .cargo/config.toml with -Tlinkall.x for xtensa target (resolves
  ROM functions, interrupt handlers, memory layout)
- Add integrated-timers feature to embassy-executor for ESP32 boards
  (resolves _embassy_time_schedule_wake)
- Add `use esp_println as _` to pull in defmt global_logger (was being
  stripped as dead code because nothing referenced the crate)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.cargo/config.toml

@@ -0,0 +1,6 @@
+[target.xtensa-esp32s3-none-elf]
+rustflags = [
+    "-C", "link-arg=-nostartfiles",
+    "-C", "link-arg=-Tlinkall.x",
+    "-C", "link-arg=-Tdefmt.x",
+]